Match the event in a silicon crystal given in List-I with its effect on the charge carriers given in List-II.
| List-I | List-II |
|---|---|
| (A) An electron of the valence band gains enough energy to cross the energy gap | (I) One free electron and one hole are lost |
| (B) An arsenic atom takes the place of a silicon atom | (II) One hole is produced, but no free electron |
| (C) A boron atom takes the place of a silicon atom | (III) One free electron and one hole are produced |
| (D) A free electron collides with a hole | (IV) One free electron is produced, but no hole |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A)-(III), (B)-(IV), (C)-(II), (D)-(I)
(A) An electron of the valence band gains enough energy to cross the energy gap — This matches (III). The electron moves into the conduction band, where it is free to move. It leaves an empty level in the valence band, and this vacancy is a hole.
(B) An arsenic atom takes the place of a silicon atom — This matches (IV). Arsenic has five valence electrons. Four of them form bonds with the silicon neighbours, and the fifth is set free. No bond is left empty, so no hole is formed.
(C) A boron atom takes the place of a silicon atom — This matches (II). Boron has only three valence electrons. The bond with the fourth neighbour is left with a vacancy, which is a hole. Boron gives no free electron.
(D) A free electron collides with a hole — This matches (I). This is recombination. The electron fills the empty bond, so the free electron and the hole both disappear.
NCERT (2026-27):
On the basis of energy bands – “… But some of the electrons from the valence band may gain external energy to cross the gap between the conduction band and the valence band. Then these electrons will move into the conduction band. At the same time they will create vacant energy levels in the valence band where other valence electrons can move. …”
n-type semiconductor – “… Thus, the pentavalent dopant is donating one extra electron for conduction and hence is known as donor impurity. …”
p-type semiconductor – “… It is obvious that one acceptor atom gives one hole. These holes are in addition to the intrinsically generated holes while the source of conduction electrons is only intrinsic generation. …”
Intrinsic Semiconductor – “… a simultaneous process of recombination occurs in which the electrons recombine with the holes. … The recombination occurs due to an electron colliding with a hole.”